Wireless communications devices are an integral part of society and permeate daily life. The typical wireless communications device includes an antenna, and a transceiver coupled to the antenna. The transceiver and the antenna cooperate to transmit and receive communications signals.
A typical radio frequency (RF) transceiver includes a power amplifier for amplifying low amplitude signals for transmission via the antenna. Given that most mobile communications devices operate on limited battery power, energy efficient power amplifiers may be desirable. More specifically and as will be appreciated by those skilled in the art, Class C and E power amplifiers are common in certain communications devices since they are efficient power amplifiers. These classes of power amplifiers are more efficient than Class A or B amplifiers, for example, but are subject to performance tradeoffs. For example, they may be nonlinear over certain frequencies and may introduce greater amounts of distortion into the amplified signal (if the signal requires a linear amplifier).
As will be appreciated by those skilled in the art, in high power amplifier applications, amplifiers are typically used to amplify signals received via transmission lines. In these applications, it may be necessary to transform the impedances of the transmission lines coupled to the input and output of the amplifier to match the load line impedance of the amplifier. As will be appreciated by those skilled in the art, the matched impedances provide greater efficiency with lower losses and greater bandwidth for the transmitted signal.
To improve the low end frequency response, magnetic materials, for example, ferrite may be added to the impedance transformer. For example, with reference to FIGS. 1-2, a ferrite impedance transformer 20 is now described. The ferrite impedance transformer 20 matches differing impedances between an input 25 and an output 26, illustratively, a 1:4 ratio. The ferrite impedance transformer 20 illustratively includes a circuit board 21, a plurality of ferrite cores 23a-23b, 24a-24b mounted on the circuit board, and a pair of rigid coaxial cables 22a-22b wound through each of the ferrite cores.
This ferrite impedance transformer 20 may suffer from several drawbacks. For example, the ferrite impedance transformer 20 may be difficult to manufacture, as the rigid coaxial cables 22a-22b are hard to manipulate. Moreover, the rigid coaxial cable 22a-22b may be expensive, and may be typically hand wound and hand soldered onto the circuit board 21. Further, given the manual labor-intensive manufacture process, the ferrite impedance transformer 20 may be subject to significant variation in electrical performance.